1. Field of the Invention
The present invention relates to an improved process for producing 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide which is known as Crystal Violet Lactone.
2. Description of the Prior Arts
Crystal Violet Lactone has been widely used as coloring agent for a pressure sensitive copying paper (carbonless copying paper). Various processes for producing Crystal Violet Lactone have been proposed. For example, it has been proposed to produce Crystal Violet Lactone by treating 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid which is called as Crystal Violet Lactone Leuko base with an oxidizing agent such as lead peroxide, potassium permanganate in an aqueous solution of a mineral acid. In accordance with this process, a large amount of black tar by-products is produced to cause a low yield of Crystal Violet Lactone and a low quality of the product of Crystal Violet Lactone.
It has been also proposed to produce Crystal Violet Lactone by oxidizing Crystal Violet Lactone Leuko base suspended in a mixed medium of a water immiscible hydrocarbon type solvent and water with hydrogen peroxide in the presence of an acid catalyst in Japanese Unexamined Patent Publication No. 78867/1977. This process has a disadvantage of difficulty of the post-treatment such as a recovery of the solvent.
It has been proposed to produce Crystal Violet Lactone by adding an aqueous solution of hydrogen peroxide to an alkaline aqueous solution of Crystal Violet Lactone Leuko base at high temperature in British Pat. No. 1,347,467. This process has a disadvantage of relatively low yield because a large amount of by-product is formed and the unreacted Crystal Violet Lactone Leuko base is remained.
It has been also proposed to produce Crystal Violet Lactone by adding a water miscible organic solvent to an alkaline aqueous solution of Crystal Violet Lactone Leuko base and oxidizing it with an oxidizing agent in U.S. Pat. No. 4,076,728. This process has a disadvantage of a difficulty of a recovery of the solvent and a low yield.
It has been also proposed to produce Crystal Violet Lactone by oxidizing Crystal Violet Lactone Leuko base with oxygen in an acidic condition in an organic solvent such as glacial acetic acid or chloroform with chloranil in the presence of a metal complex catalyst in British Pat. No. 1,395,627. This process has a disadvantage of the use of chloranil and the special organic solvent and a production of a large amount of by-products.